1. Field of the Invention
This invention resides broadly in the field of electronic musical instruments and is particularly adaptable for use in instruments employing a time-division multiplexed signal for calling forth desired tones from those available to be produced by the instrument. The principles of the present invention are applicable to any electronic musical instrument in which musical sounds are generated in response to the actuation of key switches regardless of whether those switches are actuated directly, e.g., by the musician's fingers, or indirectly, e.g., by the plucking of strings. The term key is used in a generic sense to include depressible levers, actuable on-off switches, touch or proximity responsive devices, closable apertures and so forth. The present invention relates to the generation of the complex audio waveshape of a musical note played on an electronic musical instrument. More particularly, the present invention relates to a demultiplexing waveshape generator for electronic musical instruments.
2. Description of the Prior Art
Heretofore, the art of generating audio waveshapes could be divided into two major groups. The first group and more recent in the art is that group using audio waveshape memories, either digital or analog. Typically a waveshape memory of this type is used to store a plurality of sample points which replicate the desired audio waveshape. Depending upon the system used to construct the instrument, a method of addressing the memory is provided which will read out at the required frequency selected waveshapes from memories in response to the notes called for by the user or player. Circuitry is provided to modify the waveshape as to attack and decay and other desired tonal characteristics all resulting in the final complex audio signal. The second major group in the art is that group using analog audio waveshape generators. The analog instruments are generally of two types, those using one or more discrete oscillators and those using frequency dividers for audio waveshape generation. However, the prior art method of using oscillators does not depend upon the distinction between types. Typically in an analog instrument an oscillator is used to create an audio tone. This can be done with either a free running oscillator or a voltage controlled oscillator. Circuitry is sometimes provided to modify the tone waveshape through use of filters, diodes, etc. to arrive at the desired audio waveshape. Further circuitry provides attack and decay and other desired tonal characteristics all resulting in the final complex audio signal.
The waveshape generators of the abovementioned major groups present a series of technical problems, not the least of which are the cost and the amount of hardware required to produce an acceptable audio waveshape.
Two significant advantages of the instant invention are the simplicity of the circuitry over previous audio waveshape generator systems and the cost effectiveness over previous systems.